Major strikes in the early detection, staging, monitoring, and risk stratification of men with prostate cancer have been realized over the last few decades. We have recently witnessed, for the first time, a reduction in the death rate for prostate cancer, stage migration with increased numbers of men with local/regional disease, and a greater understanding of the natural history of progression following recurrence. These advances, while not solely dependent on biomarkers, can be attributed to the discovery of Prostate-Specific Antigen (PSA) in the late 1970's. In 1999, in the wake of these discoveries, we still continue to unnecessarily biopsy 75% of men at risk for having prostate cancer to identify the 1:4 with the disease, continue to understage nearly 50% of men with presumed localized disease, continue to lack an accurate method for staging which can direct treatment decisions for the individual patient, and poorly understand the tumor biology and kinetics of disease progression. Clearly, discover of new tumor marker and validation/clinical investigation of the markers are mandatory to advance our knowledge and direct the care of men with prostate cancer. This proposal, for the development of a Clinical/Epidemiology Center, to evaluate the clinical, diagnostic and prognostic accuracy of new and existing biomarkers of prostate cancer draws strength from several unique features: a clinically important problem (see above), 2) a combined experience of over thirty years in clinical tumor marker investigation between the co-investigators, 3) collaborative efforts between our group and several commercial biomarker/reference laboratories with an interest in development and applications of biomarkers, 4) a unique resource of retrospective, prospective and longitudinal tissue and serum specimens from early detection programs, pre- and post-treatment tissue/serum banks and material from the Baltimore Longitudinal Study of Aging, 5) a history of successful clinical evaluation of tumor markers by this group which have been FDA approved and are widely used in clinical practice (e.g. PSA, percent free-PSA), 6) a history of development of clinically useful algorithms and strategies for "risk stratification" for prostate cancer and 7) an abundance of short-term, long-term, developmental, feasibility, pilot and large-scale effort projects in progress, and proposed for future development of biomarkers for prostate cancer.